MFT numbers at small apertures are irrelevant in most cases, as by F/11 virtually all modern lenses are diffraction limited anyway. You can find the diffraction limit of a lens at a certain aperture, for the Rayleigh criterion (9% contrast, the point at which a good lens can still distinguish two adjacent lines easily), by dividing the number 1600 (lp/mm) by the aperture number, e.g., for F/16 that would be 1600 lp/mm / 16 = 100 lp/mm. Multiply by 2 for the number of pixels required per mm to resolve this.
For the sensor you can use the simplified formula of 3.2 X pixel spacing in micrometer for sensor diffraction limits expressed as an aperture. If the aperture becomes smaller than the sensor diffraction limit, you will not resolve anymore detail anyway, although it may still be worthwhile to stop down further for more depth of field, provided resolution doesn't get too low.
Sensor resolution may be calculated by dividing the pixel height by the number of mm the image is high, resulting in pixels/mm, divided by two again to get resolution in lp/mm. F.e., if the sensor has 3600 pixels on the side where it is 24 mm high, it will have a pixel density of 150 pixels/mm and a resolution potential of 75 lp/mm.
You also need to take into account that overall system resolution is equal to the inverse of (1/lens resolution at f-stop used + 1/sensor resolution), all in lp/mm. If you do get below 20 lp/mm on FF, I would certainly stop closing down the aperture any further, because 20 lp/mm is the resolution average amateurs can get from their 35 mm colour negatives (good amateurs may get 40 lp/mm). Of course on APS-C, this becomes 30-35 lp/mm (and 60-70 lp/mm).
HTH, kind regards, Wim
For the sensor you can use the simplified formula of 3.2 X pixel spacing in micrometer for sensor diffraction limits expressed as an aperture. If the aperture becomes smaller than the sensor diffraction limit, you will not resolve anymore detail anyway, although it may still be worthwhile to stop down further for more depth of field, provided resolution doesn't get too low.
Sensor resolution may be calculated by dividing the pixel height by the number of mm the image is high, resulting in pixels/mm, divided by two again to get resolution in lp/mm. F.e., if the sensor has 3600 pixels on the side where it is 24 mm high, it will have a pixel density of 150 pixels/mm and a resolution potential of 75 lp/mm.
You also need to take into account that overall system resolution is equal to the inverse of (1/lens resolution at f-stop used + 1/sensor resolution), all in lp/mm. If you do get below 20 lp/mm on FF, I would certainly stop closing down the aperture any further, because 20 lp/mm is the resolution average amateurs can get from their 35 mm colour negatives (good amateurs may get 40 lp/mm). Of course on APS-C, this becomes 30-35 lp/mm (and 60-70 lp/mm).
HTH, kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....